This invention is related to the field of locking mechanisms. In particular, the invention is directed to a safety lock assembly for a door which can be locked externally and still allow a person on the interior of the door to open the lock assembly and thus the door.
It is common to provide doors with a lock to prevent unauthorized access. One such lock, which is readily available and simple to use, is a padlock latch assembly. Padlock latch assemblies include two hasps: one that is attached to the exterior of the door to be locked, and one that is attached to a fixed object, such as the door jam or the mating door of a two-door closure. The padlock is slipped through openings in the hasps, preventing them from being moved apart to any great degree. This provides a cost-effective locking mechanism that can be readily opened from the exterior of the door by one having a key. Unfortunately, once locked, there is no mechanism to open the lock from the interior of the door. This is not only inconvenient but can be particularly dangerous should there be a need to evacuate a building through the door quickly, such as during a fire. A person would need to wait until the padlock was opened before exiting. Obviously, in certain instances, this added delay could be critical.
Various lock mechanisms have been developed in the past. None of these address the problems resolved by the instant invention. U.S. Pat. No. 2,007,854 is directed to a lock for doors such as on refrigerators. A bolt positioned on the exterior of the door is biased by a spring outward to an extended position. In this extended position, the bolt engages an undersurface of a head. The head is mounted to the exterior of one door while the bolt and related parts are mounted to the exterior of the other door. A lever is pivotally mounted to a lock casing. The lever is operably engaged to the bolt such that, when the lever is rotated to an open position, the bias of the spring is overcome and the bolt is retracted, disengaging the head. An aperture in the casing is provided to receive a padlock and thus prevent the lever from being moved to the open position. A cable is attached to the bolt and extends through a passageway in the door. A ring may be provided at one end of the cable. When the cable is pulled, the bolt overcomes the bias of the spring and disengages the head.
U.S. Pat. No. 1,167,011 is directed to a door lock for barn doors. A bolt is slidingly mounted within an edge of a door. A spring biases the bolt into an extended position such that it engages a cavity in a doorpost. Handles are pivotally mounted to the door and to the bolt. One handle is positioned on the interior of the door; the other handle is positioned on the exterior of the door. When either handle is rotated outwardly, it causes the bolt to be retracted overcoming the spring bias. Once retracted, the door can be swung to an open position. A hasp is provided at the exterior of the door to receive a pad lock and thus prevent the exterior handle from rotating.
U.S. Pat. No. 1,763,694 is directed to a deadbolt intended particularly for doors or windows that swing open from the top. A hollow bolt member cooperates with a catch to engage an angled piece. The catch is biased to a forward or locked position by a spring. A rod is pivotally mounted to the catch at one end and connected to a pull chain at the other. The pull chain is connected to an arm, which is positioned in a slot in the door. The arm is connected to an exterior handle. When the handle is pulled, the arm is displaced. The displacement of the arm causes the pull chain to move, overcoming the bias of the spring and retracting the catch thereby disengaging the angled piece. One the interior of the door, a thumb piece is pivotally mounted to the door proximate the arm. When the thumb piece is rotated, it also causes the displacement of the arm and the disengagement of the catch. There is no teaching of using a padlock with this door assembly.